Sylvania



UNITED STATES PATENT? OFFICE JOHN G. SCHMIDT, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO E. F. HOUGHTON AND COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENN- SYLVANIA PRODUCT AND PROCESS FOR PREVENTING THE SOLVENT ACTION OF SULPHUBIC ACID N IRON AND STEEL No Drawing. Application filed Iarch 21, 1928, Serial No. 263,594. Renewed April 28, 1980.

My invention relates to a product and process for preventing the solvent action of sulphuric acid on iron and steel, and more particularly to a new pickling solution which Wlll effectively remove scale and rust from iron and steel without attacking the surface of the iron or steel.

The principal object of my invention is to provide a solution of sulphuric acid in which the pitting and corrosion action of the acid on iron and steel will be reduced to a minimum, if not completely precluded. A further object of my invention is to provide a solution of sulphuric acid which will be relatively inert towards the ferrous metals and therefore can'be shipped in iron or steel con- .tainers with assurance that the corrosion of the containers will be minimized or prevented.

Still another object of my invention is to provide a method of pickling and a pickling bath which will most effectively and efficiently remove the scale and rust from iron and steel without pitting or corroding the surface of the object being treated. Other objects will appear from a consideration of the specification and claims.

Sulphuric acid per se readily attacks iron and steel and therefore great diificulties are encountered in the shipping of this acid. If iron or steel containers are used, the length of their life is short and there is always present the hazard of leakage with its attending danger to property and human life. In the so-called pickling processes, sulphuric acid is used to remove the scale or rust from the surface of the iron or steel. In order to be of practical use, however, the surface of the iron and steel must remain bright and smooth for otherwise the objects are unfit for galvanizing and use in the trade. The sulphuric acid first removes the scale and rust but,when thesehave been removed, it attacks the metal below, pitting and roughening the surface thereof with the accompanying evolution of disagreeable gases which endanger the health of the workman. It is not possible in commercial practice to remove the scale or rust without also attacking the metal for there is no indication when the process should be stopped. ur-

thermore, the rust and scale usually do not cover the metal surface uniformly and therefore the acid dissolves the scale at one point on the surface while at some adjacent point where the scale has been removed, the surface 55 of the metal is attacked by the acid.

My invention is characterized by the addition of a new compound to the sulphuric acid, which compound will minimizEoFpievent the acid from attacking the iron or steel surface without reducing the effectiveness of the acid in removing the scale and rust. I am aware that so-called inhibitors of various types have previously been suggested for this use, but the use of the compounds of the present invention has many advantages over those heretofore known. The class of compounds of the present invention are much more effective, easier to handle, and are completely stable in the sulphuric acid.

My invention contemplates the addition of reactionmprodgcts of aryl thioureas and aldeh des to the sulphuric acid. Theadditi'oh of these compounds in relatively small amounts practically prevents any pitting or corrosion action of the sulphuric acid on iron and steel. By the term reaction products of aryl thioureas and aldehydes, I include reaction products resulting from the chemical combination of an aromatic thiourea, such astliiocarbanilide and di-ortho-tolyl thiourea, alfd'anya'liphatic aldehyde, such as formaldehyde, acetaldehyde,f'lpropylaldehyde, allyl a dehyde, and the like, or aromatic aldehyde, such'asfbpnzaldehyde or cinnamic aldehyde, tli'efir'fhomologues, isomers -or substitution products.

As a typical example, I will describe the reaction between di-ortho-tolyl thiourea and formaldehyde. In a typical case, I place in a 2 liter flask under a water reflux condenser 256 grams of dim tho-tolyl thiourea, 150 grams of 40% ormaldeli deiolution, and 200 cubic centimeters 0 water. The mixture is boiled and refluxed, and after a few hours, the crystals of the di-ort-ho-tolyl thiourea begin to disappear with the accompanying formation of a heavy oily compound which sinks to the bottom of the flask. After 16-18 hours refluxing, the reaction is complete and the crystals of the di-ortho-tolyl thiourea have entirely disappeared. The oily compound is separated from the supernatant water and is ready for immediate use or it may be subjected to distillation prior to its use. The new compound is a colorless, heavy liquid, very viscous at ordinary temperatures, very slightly soluble in cold water and only sparingly soluble in boiling water. It is readily soluble in ether, benzol, chloroform, acetone, carbon tetrachloride and boiling alcohol. Qualitative tests show an absence of an aldehyde and of thiourea in the resulting pure product. In the commercial manufacture of the reaction products, an excess of formaldehyde is used in order to cause the reaction to be complete hence in the commercial product small amounts of the occluded or retained aldehyde may be detected. The product boils under diminished pressure without decomposition and may be distilled. Up to the present time all attempts to crystallize the product have failed.

Various other methods might be used to obtain the reaction product between the aryl thiourea and the aldehyde. lVhile I have described the reaction between di-ortho-tolyl thiourea and formaldehyde, the same process is applicable for the preparation of other reaction products, such, for example, as the reaction product of thiocarbanilide and formaldehyde or the reaction product between di-ortho-tolyl thiourea and benzaldehyde. These last two named reaction products are solids of a whitish cast, are very slightly soluble in water, and are soluble in the various organic solvents. Qualitative tests on these reaction products also show an entire absence of thiourea and aldehyde groups.

These reaction products of aryl thioureas and aldehyde are excellent inhibitors and have markedly improved properties over the inhibitors heretofore known and used.

The percentages of the reaction products of an aryl thiourea and an aldehyde to be added to the sulphuric acid may vary considerably, depending somewhat on the nature of the pieces being treated and the amount of scale or rust to be removed. Tests have shown as small a proportion as one part of the new condensation products of di-ortho-tolyl thiourea and formaldehyde to 1,100 parts of sulphuric acid of 98% strength, or one part of the above reagent to 22,000 parts of a 5% sulphuric acid solution, is quite effective. The amounts added may be increased considerably but for all practical purposes, the percentage needs never to exceed 1%. Corresponding proportions of the other reaction products of an aryl thiourea and an aldehyde may be used efiectively.

The, efiectiveness of the reaction products is shown in the following test, in which two glass beakers holding 2 liters were each charged with 1500 grams of a 5% sulphuric acid solution. To one beaker was added 124: milligrams of the condensation product of di-ortho-tolyl thiourea and formaldehyde above described. The other beaker contained only the acid solution. Both were then heated to boiling temperature and a strip of steel 8 x 1 x inch was placed in each and the temperature was kept near the boiling point for one hour. Volumes of hydrogen were given off from the steel in the beaker containing no reaction product, while practically none was evolved from the steel rendered passive by the reaction product. At the end of one hour the strips of steel were taken from the beakers and compared. The strip immersed in the acid alone was badly corroded and eaten away, while the strip which had been rendered immune to the acid by the addition of the reaction product remained clean, bright, and unaffected by the acid.

Considerable modification is possible in the choice of the reaction products of an aryl thiourea and an aldehyde, and in the percentages used with the sulphuric acid without departing from the essential features of the invention.

I claim:

1. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a solution of sulphuric acid to which has been added a reaction product of an aryl thiourea and an aldehyde.

2. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a solution of sulphuric acid to which has been added a reaction product of di-ortho-tolyl thiourea and formaldehyde.

3. A pickling bath for removing scale and rust from iron and steel comprising sulphuric acid and 1% or less of a reaction product of an aryl thiourea and aldehyde.

4. A pickling bath for removing scale and rust from iron and steel comprising sulphuric acid and 1% or less of a reaction product of di-ortho-tolyl thiourea and formaldehyde.

5. The process of pickling iron and steel objects which comprises subjecting said ob jects to the action of a solution of sulphuric acid to which has been added a reaction product of a thiourea and a compound containing an aldehyde group.

6. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a, solution of sulphuric acid to which has been added a reaction product of a substituted thiourea and a compound containing an aldehyde group.

7. The process of pickling iron and steel objects which comprises subjecting said objects to the action of a solution of sulphuric acid to which has been added a reaction product of an aryl substituted thiourea and a compound containing an aldehyde group.

404. bUIVHUSI I IUNS,

8. A pickling bath for removing scale and rust from iron and steel comprising sulphuric acid and a small proportion of the reaction product of a thiourea and a compound containing an aldehyde group.

9. A pickling bath for removing scale and rust from iron and steel comprising sulphuric acid and a small proportion of the reaction product of a substituted thiourea and a compound containing an aldehyde group.

10. A pickling bath for removing scale and rust from iron and steel comprising sulphuric acid and a small proportion of the reaction product of an aryl substituted thiourea and a compound containing an aldehyde group.

JOHN G. SCHIHDT.

examiner 

